It's easy to miss how important this launch is. SpaceX builds rockets but lots of organizations around the world have built and continue to build rockets that do everything that this rocket did, and sometimes more. But in some ways that's also why this launch is impressive.
SpaceX is a private company that has developed its launch vehicles outside of a conventional government procurement program, on their own terms. The typical way that anything gets done in the space launch business is that a government organization develops plans and dedicates a budget and then contracts with companies for procurement. In the end it's still a private company developing a launch vehicle whether it's Lockheed-Martin or SpaceX so again this may seem very similar on the surface. But the differences in character have a huge number of effects. Government directed development is bureaucratic, it's expensive, it's risk averse, and it's often inflicted with institutional superstitions and fads. Even worse it tends to rely on a "big design up front" or "waterfall" development model. Commercial development tends to be extremely pragmatic and iterative, leading to improved results.
Look at the Atlas V and Delta IV for example. Both have been in service for about a decade, after being developed through a government procurement program, and both have not seen significant changes in their design during their operational period. Compare that to the story at SpaceX who have developed 5 different rocket engines and 5 different launchers in the decade or so they've been operating. The SES-8 launch represents only the second launch of a new iteration of the Falcon 9 rocket, the v1.1, which uses new engines, a new thrust support structure, stretched fuel tanks, a new ignition system, and is designed to be capable of re-use of the first stage with the addition of landing legs.
Let's imagine a hypothetical parallel universe SpaceX. They could have put a Falcon Heavy into production based on the Falcon 9 v1 core, or they could have made less ambitious changes to the Falcon 9 v1.1 while retaining the same performance levels. With such a lineup they would still have a very bright financial future ahead of them. Their low manufacturing and operational costs enable them to offer similar launch services to the competition at much lower prices. With the offerings I've described SpaceX could easily become a multi-billion dollar company with very healthy profit margins. But SpaceX has grander ambitions than just making money, they want to open up the spaceflight market and they want to kickstart manned exploration of Mars.
This mission is a bit of a demonstration that their ambition has not gone too far, that they are actually capable of delivering on their promises and, crucially, that they can deliver satellite payloads to orbit just as well as anyone.
What does that mean? In the simplest sense it means that SpaceX's bank account is going to get pretty fat over the next few years. A corporation getting wealthy isn't a big deal right? Except in this case that profit isn't just going to be spent on yachts and mansions and private jets, much of it will be re-invested in the company in order to further the company's (and its founder's) vision.
At most rocket companies making rockets is an excuse to make money. At SpaceX making money is an excuse to make more rockets. They're going to develop and prove reusability of the Falcon 9 v1.1 first stage "live" as it were using operational missions. They've already used operational cargo delivery missions to flight-proof a substantial portion of the manned capsule hardware they've been working on. Over the next few years they are going to bring into service first stage reusability, the Falcon Heavy (and then later bring reusability into that platform as well), and the manned Dragon. Meanwhile they're developing LOX/Methane fueled engines for their next generation launchers which should be highly reusable (since Methane burns so cleanly) and be targeted at Manned Mars missions. Most space launch companies are content with sitting at comfortable plateaus and waiting for government encouragement, and funding, to step up to the next plateau, but SpaceX is a company that has constant innovation in its blood.
This mission validates the work they've done and their development style while also providing a huge signal to the industry that SpaceX is a reliable carrier. Which will help to funnel a lot more business their way and give them more excuses to build and develop more rockets, culminating in launch costs a fraction of what is possible today and catalyzing manned exploration of the Solar System.